Apparatus and Method for Writing onto an Audio CD, and Audio CD

ABSTRACT

Parametric multichannel information is written onto a normal standard audio compact disc, e.g. in the user subchannels, so that the CD enables normal stereo reproduction with a normal reproduction device, or multichannel reproduction with a supplementary device which is easy to connect and which reads out both the stereo information and the parametric multichannel information from the audio CD actually conforming with the standard, and reconstructs more than two audio channels therefrom.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of copending InternationalApplication No. PCT/EP2005/001650, filed Feb. 17, 2005, which designatedthe United States, and was not published in English and is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to stereo audio CD technology, and inparticular to apparatus and methods for writing onto audio CDs andrespective methods and apparatus for retrieving data from CDs.

2. Description of Prior Art

Recently, multichannel audio reproduction technology has becomeincreasingly important. This may be due to the fact that audiocompression/coding technologies such as the prior art MP3 technologyhave allowed transmitting audio data via the internet or othertransmission channels with a limited bandwidth. The MP3 codingtechnology has become so famous because of the fact that it enables allrecordings to be distributed in a stereo format, i.e. in a digitalrepresentation of the audio recording, which includes a first, or left,stereo channel and a second, or right, stereo channel.

Alternative media for distributing stereo data are the prior-art audioCDs. The digital compact discs developed from the cooperation of Philipsand Sony is based on contactless optical scanning, by means of laser, ofa disc, which is recorded on one side, as an information carrier. In theCD player, for reading out, the beam of a semiconductor laser which isreflected by the disc and modulated in its intensity is received by aphotodiode. The output signal of the photodiode is converted into aserial data signal, and the clock signal is obtained therefrom. Whatfollows is the separation of the synchronization characters and there-conversion of the channel code into data, test characters andcontrol/display bits. The control/display decoder provides the signalsfor motor speed, focusing and track-following as well as for finding anddisplaying certain places in music. In the error-protection decoder, anydisturbed signal information interfered with might be supplemented bymeans of the check bits. After separating the data stream by means ofthe multiplexer, the digital/analog reconversion into the analog audiosignal of the left and right channels is performed.

In accordance with the standardized CD frame structure which is sharedby all audio CDs with stereo information, and to which common CD playersare set, there are six successive samples of the left and right channelsin one frame, respectively. Transmission starts with the left channel ineach case. Each 16-bits sample starts with the MSB and is divided intotwo audio symbols of 8 bits each. The stereo data is subjected to errorprotection coding with a two-step, so-called CIRC method.

Nevertheless, fundamental disadvantages of conventional 2-channel soundsystems exist. Therefore, so-called surround technology has beendeveloped. A recommended multichannel surround representation includesan additional center channel C and two surround channels Ls, Rs inaddition to the two stereo channels L and R. This reference tone formatis also referred to as 3/2 stereo, which means that there are threefront channels and two surround channels. Generally, five transmissionchannels are required. In a reproduction environment, at least fiveloudspeakers are required at the respective five different places inorder to obtain an optimum so-called “sweet spot” at a specific distancefrom five accurately placed loudspeakers.

In the area of CD technology, so-called DVDs have found widespreadacceptance. They typically contain a complete 5.1 or 7.1 recording, i.e.a complete representation of each individual sound channel.

What is disadvantageous about DVDs, however, is the fact that specificDVD players are required for them, and that conventional audio CDplayers thus cannot be used to play back DVDs. In addition, there isalso no possibility of upgrading such normal audio CD players withsimple measures, so that they would be able to not only play back audioCDs but also DVDs.

This is unfortunate especially because there are a large number of CDplayers in circulation with which a multichannel reproduction cannot beachieved. On the other hand, however, many customers shy back from“sorting out” the fully functional CD player with which they arefamiliar and fully contented to now change to DVDs only, even though thecustomers might not be interested at all in the video informationtypically contained in the DVDs, but might simply want to have a good5-channel sound.

It is true that coded multichannel representations obtained via theinternet or from other sources might be burned onto CDs, provided thatno licensing rights are violated. But such burned CDs, too, are notcompatible with normal CD players since they contain coded information,whereas the stereo data contained on the audio CDs is merelyuncompressed 16-bits PCM data which is merely subjected to errorprotection coding, which leads to an increase of the data rate, ratherthan being subjected to data compression, which would lead to areduction in the data rate.

Thus, in technology there are many techniques for reducing the amount ofdata required for transmitting a multichannel audio signal. Suchtechniques are referred to as joint stereo techniques. To this end,reference shall be made to FIG. 3 which depicts a joint stereo apparatus60. This apparatus may be an apparatus which implements, for example,intensity stereo (IS) technique or binaural cue coding technique (BCC).Such a device typically receives, as the input signal, at least twochannels CH1, CH2, . . . , CHn, and outputs one single carrier channelas well as parametric multichannel information. The parametric data isdefined such that an approximation of an original channel (CH1, CH2, . .. , CHn) may be calculated in a decoder.

Normally, the carrier channel will include subband samples, spectralcoefficients, time domain samples, etc. which provide a relatively finerepresentation of the underlying signal, whereas the parametric dataincludes no such samples or spectral coefficients but includes controlparameters for controlling a certain reconstruction algorithm, such asweighting by multiplying, by time-shifting, by frequency-shifting, etc.The parametric multichannel information therefore includes a relativelycoarse representation of the signal or of the associated channel. Innumbers, the amount of data required by a carrier channel is an amountfrom about 60 to 7o kbits/s, whereas the amount of data required byparametric side information for a channel ranges between 1.5 and 2.5kbits/s. It shall be noted that the above numbers apply to compresseddata. Naturally, a non-compressed CD channel requires data rates in therange of about 10 times the said amount. An example of parametric dataare the prior-art scale factors, intensity stereo information or BCCparameters, as will be set forth below.

The technique of intensity stereo coding is described in the AESpreprint 3799, “Intensity Stereo Coding”, J. Herre, K. H. Brandenburg,D. Lederer, February 1994, Amsterdam. Generally, the concept ofintensity stereo is based on a main axis transformation to be performedon data of both stereophonic audio channels. When most data points areconcentrated around the first main axis, a coding gain may be achievedin that both signals are rotated by a certain angle before the codingtakes place. However, this is not always given for real stereophonicreproduction techniques. Therefore, this technique is modified to theeffect that the second orthogonal component is excluded from thetransmission in the bitstream. Thus, the reconstructed signals for theleft and right channels consist of differently weighted or scaledversions of the same signal transmitted. Nevertheless, the reconstructedsignals differ with regard to their amplitudes, but they are identicalwith regard to their phase information. The energy/time envelopes ofboth original audio channels, however, are maintained by the selectivescaling operation which typically operates in a frequency-selectivemanner. This corresponds to human perception of sound at highfrequencies, where the dominant spatial information is determined by theenergy envelopes.

In practical implementations, the signal transmitted, i.e. the carrierchannel, is additionally generated from the aggregate signal of the leftand right channels rather than the rotation of both components. Inaddition, this processing, i.e. the generation of intensity stereoparameters, is performed, for performing the scaling operations, in afrequency-selective manner, i.e. independently for each scale factorband, i.e. for each coder frequency partition. Preferably, both channelsare combined to form a combined, or “carrier”, channel and, in additionto the combined channel, the intensity stereo information. The intensitystereo information depends on the energy of the first channel, theenergy of the second channel or the energy of the combined channel.

The BCC technique is described in the AES Convention Paper 5574“Binaural Cue Coding applied to stereo and multichannel audiocompression”, T. Faller, F. Baumgarte, May 2002, Munich. In BCC coding,a number of audio input channels are converted into a spectralrepresentation, specifically using a DFT-based transformation withoverlapping windows. The resulting spectrum is partitioned intonon-overlapping portions, each of which has an index. Each partition hasa bandwidth proportional to the equivalent square bandwidth (ERB). Theinter channel level differences (ICLD) and the inter channel timedifferences (ICTD) are determined for each partition and for each framek. The ICLD and ICTD are quantized and coded so as to pass, eventually,into a BCC bitstream as side information. The inter channel leveldifferences and the inter channel time differences are given in relationto a reference channel for each channel. Subsequently, the parametersare calculated in accordance with predetermined formulae which depend onthe specific partitions of the signal to be processed.

On the decoder side, the decoder typically receives a mono signal andthe BCC bitstream. The mono signal is transformed into the frequencydomain and is input into a spatial synthesis block which also receivesdecoded ICLD and ICTD values. In the spatial synthesis block, the BCCparameters (ICLD and ICTD) are used to perform a weighting operation ofthe mono signal to synthesize those multichannel signals which, after afrequency/time conversion, represent a reconstruction of the originalmultichannel audio signal.

In the case of BCC, the joint stereo module 60 is operative to outputthe channel-side information such that the parametric channel data isquantized and coded ICLD or ICTD parameters, one of the originalchannels being used as a reference channel for coding the channel-sideinformation.

Normally, the carrier signal is formed from the sum of the participatingoriginal channels.

Naturally, the above techniques provide only a mono representation for adecoder which can process the carrier channel only but is not able toprocess the parametric data for generating one or several approximationsof more than one input channel.

The BCC technique is also described in the US patent publications US2003/0219130 A1, US 2003/0026441 A1 and US 2003/0035553 A1. In addition,reference shall be made to the specialist publication “Binaural CueCoding. Part II: Schemes and Applications”, T. Faller and F. Baumgarte,IEEE Trans. On Audio and Speech Proc. Vol. 11, No. 6, November 2003.

A typical BCC scheme for multichannel audio coding will be representedin more detail below, specifically with reference to FIGS. 4 to 6.

FIG. 5 shows such a BCC scheme for coding/transmitting multichannelaudio signals. The multichannel audio input signal at an input 110 of aBCC coder 112 is downmixed in a so-called downmix block 114. In thisexample, the original multichannel signal at the input 110 is a5-channel surround signal with a front left channel, a front rightchannel, a left surround channel, a right surround channel and a centerchannel. In the preferred embodiment of the present invention, downmixblock 114 generates an aggregate signal by simply adding up these fivechannels into a mono signal.

Other downmixing schemes are known in the art, so that using amultichannel input signal results in a downmix channel having a singlechannel. This single channel is output at an aggregate-signal line 115.A piece of side information obtained from the BCC analysis block 116 isoutput on a side information line 117.

In the BCC analysis block inter channel level differences (ICLD) andinter channel time difference (ICTD) are calculated as has beenrepresented above. As of late, the BCC analysis block 116 is also ableto calculate inter channel correlation values (ICC values). Theaggregate signal and the side information are transmitted to a BCCdecoder 120 in a quantized and coded format. The BCC decoder decomposesthe transmitted aggregate signal into a number of subbands and performsscalings, delays and other processing steps to supply the subbands ofthe multichannel audio channels to be output. This processing isperformed such that the ICLD, ICTD and ICC parameters (cues) of areconstructed multichannel signal at the output 121 match the respectivecues for the original multichannel signal at the input 110 in the BCCcoder 112. For this purpose, BCC decoder 120 includes a BCC synthesisblock 122 and a side information revision block 123.

The internal structure of the BCC synthesis block 122 will berepresented below with reference to FIG. 6. The aggregate signal on line115 is fed to a time/frequency conversion unit or filter bank FB 125. Atthe output of block 125, there are a number N of subband signals or, inan extreme case, a block of spectral coefficients when the audio filterbank 125 performs a 1:1 transformation, i.e. a transformation generatingN spectral coefficients from N time domain samples.

The BCC synthesis block 122 further includes a delay stage 126, a levelmodification stage 127, a correlation processing stage 128 and aninverse filter bank stage IFB 129. At the output of stage 129, thereconstructed multichannel audio signal having, for example, fivechannels in the event of a 5-channel surround system, may be output to aset of speakers 124 as are represented in FIG. 5 or FIG. 4.

The input signal sn is converted to the frequency range or the filterbank range by means of the element 125. The signal output by element 125is copied such that several versions of the same signal will beobtained, as is represented by the copying node 130. The number ofversions of the original signal equals the number of output channels inthe output signal. Then each version of the original signal issubjected, at node 130, to a certain delay d₁, d₂, . . . , d_(i), . . .d_(N). The delay parameters are calculated by the side informationprocessing block 123 in FIG. 5 and are derived from the inter channeltime differences as have been calculated by the BCC analysis block 116of FIG. 5.

The same applies to multiplication parameters a₁, a₂, . . . , a_(i), . .. , a_(N) which are also calculated by the side information processingblock 123 on the basis of the inter channel level differences as arecalculated by BCC analysis block 116.

The ICC parameters calculated by the BCC analysis block 116 are used forcontrolling the functionality of block 128, so that certain correlationsbetween the signals which are delayed and manipulated in their levelsare obtained at the outputs of block 128. It shall be noted here thatthe order of stages 126, 127, 128 may deviate from the order shown inFIG. 6.

It shall be pointed out that with frame-wise processing of the audiosignal, the BCC analysis is also performed in a frame-wise, i.e.temporally variable, manner and that, in addition, a frequency-wise BCCanalysis is obtained, as may be seen from the filter band partitioningfrom FIG. 6. This means that the BCC parameters are obtained for eachspectral band. This means further that in the event that the audiofilter bank 125 decomposes the input signal into, for example, 32bandpass signals, the BCC analysis block will obtain a set of BCCparameters for each of the 32 bands. Of course, BCC synthesis block 122of FIG. 5, depicted in detail in FIG. 6, performs a reconstruction whichis also based on the 32 bands mentioned by way of example.

With reference to FIG. 4, a scenario will be presented below which isused to determine individual BCC parameters. Normally, the ICLD, ICTDand ICC parameters may be defined between pairs of channels. However, itis preferred to determine the ICLD and ICTC parameters between areference channel and any other channel. This is depicted in FIG. 4A.

ICC parameters may be defined in various manners. Generally speaking,ICC parameters in the coder may be determined between all possible pairsof channels, as is shown in FIG. 4B. However, it has been proposed tocalculate only ICC parameters between the two most powerful channels atany time, as is shown in FIG. 4C, which depicts an example wherein anICC parameter between channels 1 and 2 is calculated at one time, and anICC parameter between channels 1 and 5 is calculated at another time.Subsequently, the decoder synthesizes the inter channel correlationbetween the most powerful channels in the decoder and uses certainheuristic rules for calculating and synthesizing the inter channelcoherence for the remaining pairs of channels.

With regard to calculating, for example, the multiplication parametersa₁, a_(N) on the basis of the ICLD parameters transmitted, referenceshall be made to the AES convention paper No. 5574. The ICLD parametersrepresent an energy distribution of an original multichannel signal.Without loss of generality, it is preferred, as depicted in FIG. 4A, totake four ICLD parameters which represent the energy difference betweenthe respective channels and the front left channel. In the sideinformation processing block 122, the multiplication parameters a₁, . .. , a_(N) are derived from the ICLD parameters in such a manner that theentire energy of all reconstructed output channels is the same (or isproportional to the energy of the aggregate signal transmitted).

In order to put multichannel information onto CDs, one may also fallback, beside the DVDs provided, to special audio CDs which store thesound channels in a data-reduced form using audio coding methods such asDTS. These special audio CDs cannot be played back on normal audio CDplayers, but require a decoder of their own which in most cases is to beconnected externally to the digital output of the normal audio CDplayer.

In addition, there are hybrid SACDs which offer, by means of two layerson the CD, both the conventional stereo sound for reproduction on audioCD players (in one of the layers) and the multichannel sound in the DSCformat (in the other layer) for reproduction on SACD players.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a flexible conceptfor spreading and generating multichannel audio data, the conceptpotentially achieving a high level of market acceptance.

In accordance with a first aspect, the invention provides an apparatusfor writing audio information, from which a multichannel audiorepresentation may be reconstructed, onto a compact disc, the apparatushaving:

a writer for writing parametric multichannel information onto one orseveral locations of the CD which are not used for two base channelsincluding a two-channel representation of the audio information, theparametric multichannel information being configured such that, togetherwith the two base channels, it enables a multichannel audiorepresentation with more than two audio channels.

In accordance with a second aspect, the invention provides a compactdisc including audio information, the audio information including twobase channels and parametric multichannel information, wherein themultichannel information is written onto locations on the compact discwhich are not taken up by the two base channels, the parametricmultichannel information being configured such that, together with thetwo base channels, it enables a multichannel audio representation withmore than two audio channels.

In accordance with a third aspect, the invention provides an apparatusfor playing back a compact disc with audio information, the audioinformation including two base channels and parametric multichannelinformation, wherein the multichannel information is written ontolocations on the compact disc which are not taken up by the two basechannels, the parametric multichannel information being configured suchthat, together with the two base channels, it enables a multichannelaudio representation with more than two audio channels, the apparatushaving:

a reader for reading out the two base channels and for reading out theparametric multichannel information; and

a reconstructor for reconstructing a multichannel representation on thebasis of the two base channels and the parametric multichannelinformation.

In accordance with a fourth aspect, the invention provides a method forwriting audio information, from which a multichannel audiorepresentation may be reconstructed, onto a compact disc, the methodincluding the steps of:

writing parametric multichannel information to one or several locationsof the CD which are not provided for two base channels which include atwo-channel representation of the audio information, the parametricmultichannel information being configured such that, together with thetwo base channels, it enables a multichannel audio representation withmore than two audio channels.

In accordance with a fifth aspect, the invention provides a method forplaying back a compact disc with audio information, the audioinformation including two base channels and parametric multichannelinformation, wherein the multichannel information is written ontolocations on the compact disc which are not taken up by the two basechannels, the parametric multichannel information being configured suchthat, together with the two base channels, it enables a multichannelaudio representation with more than two audio channels, the methodincluding the steps of:

reading out the two base channels and reading out the parametricmultichannel information; and

reconstructing a multichannel representation on the basis of the twobase channels and the parametric multichannel information.

In accordance with a sixth aspect, the invention provides a computerprogram having a program code for performing the method for writingaudio information, from which a multichannel audio representation may bereconstructed, onto a compact disc, the method including the steps of:

-   -   writing parametric multichannel information to one or several        locations of the CD which are not provided for two base channels        which include a two-channel representation of the audio        information, the parametric multichannel information being        configured such that, together with the two base channels, it        enables a multichannel audio representation with more than two        audio channels,        when the program runs on a computer.

In accordance with a seventh aspect, the invention provides a computerprogram having a program code for performing the method for playing backa compact disc with audio information, the audio information includingtwo base channels and parametric multichannel information, wherein themultichannel information is written onto locations on the compact discwhich are not taken up by the two base channels, the parametricmultichannel information being configured such that, together with thetwo base channels, it enables a multichannel audio representation withmore than two audio channels, the method including the steps of:

-   -   reading out the two base channels and reading out the parametric        multichannel information; and    -   reconstructing a multichannel representation on the basis of the        two base channels and the parametric multichannel information,        when the program runs on a computer.

The present invention is based on the findings that on a common audio CDin accordance with the normal CD format, subchannels are provided whichare defined in accordance with the CD standard to transmit metainformation, such as data and text and/or a video image. In accordancewith the invention, these subchannels are utilized for also writingparameter information onto the normal stereo audio CD so that a normalstereo audio CD includes sufficient information for multichannelreproduction.

One advantage of this concept is that it is compatible with common CDplayers. Common CD players then will continue to provide a stereo soundrepresentation of the normal audio CD stereo data which is notinfluenced by the inventive concept. However, if a CD player is equippedin accordance with the invention, i.e. with a small supplementary modulewhich receives, at the CD player on the output side, the stereo data inaddition to the subchannel data, i.e. the multichannel parameter data,and calculates the parameter data and the stereo data with one anotherusing the underlying reconstruction algorithm, a multichannelrepresentation of the original multichannel signal will be provided.

This is to achieve that a user may keep his/her normal CD player whichhe/she has got used to and with which he/she is satisfied and, forreading the multichannel audio CDs, will require only the supplementarymodule which, however, may readily be connected to the CD player sinceeach CD player has a stereo output. Thus, the supplementary module neednot intervene in the CD player but may simply be plugged in at theterminal which is provided by the CD player anyway. Preferably thisterminal, or output, of the CD player is a digital output. However, if aCD player has an analog output only, which may be the case with very oldmodels, one would additionally require an analog/digital converter inthe supplementary multichannel module.

In addition, the present invention is advantageous in that the CD isbackward-compatible in a backward-compatible recording of themultichannel information, i.e. that it may also be played back on astereo CD player of a conventional type. The inventive CD may thus beplayed back both on a normal CD player and on a CD player expanded to amultichannel CD player.

Alternatively, the multichannel parameter information may also beaccommodated in other places of the audio CD which are not occupied bythe two-channel representation, for example in a still vacant locationof the CD, on a data partition of a hybrid CD, in a separate session atthe end of the CD, etc.

It is preferred, however, to “hide” the parameter data onto thesubchannels already provided by the normal audio CD standard anywaybecause no interventions in CDs whatsoever are planned and because theCDs fully comply with the standard despite having multichannel soundinformation now, and because they thus do not cause any problems inplayback devices.

The inventive concept is further advantageous in that the amount of datais sufficiently compressed due to the multichannel information beingrepresented by parametric multichannel data, so that the channelcapacity of the subchannels on the CD is sufficiently large. Of course,it would not be possible to store, on these subchannels, anynon-parameter information as are found on DVDs.

A further advantage of the present invention is that existing CD writingdevices can be used, since anyway they have already been designed towrite data into the user subchannels.

Moreover, existing CD playback devices may be used which are designedfor reading from subchannels.

Thus, a stereo CD may be turned into a multichannel CD having at least 3and preferably 5, 7 or still more channels at minimum expense on thepart of the CD manufacturer, with regard to the CD itself as well as onthe part of the user. All of this is achieved using the tried and testedaudio CD technology which has been refined, well-tried and accepted foryears, which is something that cannot be said without reserve for recenttechnologies, in particular in the field of DVDs.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe accompanying drawing, in which:

FIG. 1 is a block diagram of the inventive apparatus for writing onto acompact disc;

FIG. 2 is a block diagram of an inventive apparatus for playing back acompact disc;

FIG. 3 is a prior art joint stereo coder for generating channel data andparametric multichannel information;

FIG. 4 is a representation of a scheme for determining ICLD, ICTD andICC parameters;

FIG. 5 is a block diagram representation of a BCC coder/decoder chain;and

FIG. 6 is a block diagram of an implementation of the BCC synthesisblock of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an inventive apparatus for writing audio information fromwhich a multichannel audio representation may be reconstructed onto acompact disc using a means for writing parametric multichannelinformation at one or several locations of the CD which are not providedfor two base channels which include a two-channel representation of theaudio information.

In particular, the parametric multichannel information which is notwritten onto the CD by means 10 is configured such that it enables,along with the two base channels, a multichannel audio representationwith more than two audio channels. Preferably, a parametric multichannelinformation is BCC parameters or intensity stereo parameters or otherparametric data which, unlike the two stereo base channels, is merely acoarse representation of a channel of the original multichannel audiosignal.

Depending on the embodiment, the CD is equipped with the parametricmultichannel information with normal stereo data already before beingwritten onto. This would be the case if the multichannel informationwere subsequently written onto the CD. However, it is preferred tointroduce unwritten audio CDs into the inventive apparatus for writing,such that the inventive apparatus comprises also a means 12 for writingstereo data in accordance with the CD standard. For reasons ofillustration only, the two means for writing are depicted as separatemeans in FIG. 1. Naturally, they may be implemented by the same physicalCD writing device.

The product of the inventive apparatus is a CD 14 including theabsolutely normal stereo base channels in locations on the CD which areprovided for the stereo information, as is depicted at 16 a. However, incontrast to a normal CD, multichannel parameter information such as 5.1parameter information, 7.1 parameter information, etc. is present atlocations to which the stereo information has not been written, i.e. ata location 16 b. This parameter information is preferably BCC parameterdata, as has already been set forth.

In a preferred embodiment of the present invention, the parameter datais stored, synchronously with the normal stereo data, in asector-by-sector manner on the audio CD in the “subchannels” R, S, T, U,V, W available on the audio CD. A description of the subchannels and ofthe CD data format is found in the textbook “Audio-Handbuch derSchaltungstechnik”, Paul Skritek, Franzis-Verlag, 1988, chapter 17“Kompakt-Disk-Technik”, pages 329-338.

Normally, these subchannels are intended to store information about theCD, including the table of contents and the current time of the trackfor the indication of the reproduction device. Alternatively, thesechannels may also be used to store graphical representations with lowresolutions and output them on respective reproduction devices. Thesesubchannels, or the sub-codes stored on the subchannels, may also beused to store additional information as is required, for example, forkaraoke CDs.

In accordance with the invention, however, these subchannels are nowused to “upgrade” the payload data itself, i.e. the stereo basisinformation, in that parametric multichannel information is stored inthe subchannels. In terms of the data rate, the gross data rateavailable amounts to 7.36 kbps. Since there are six user data channelsavailable, a total data rate of 44.1 kbps is thus available. This is avalue which is even higher than the amount of data typically required bythe BCC parameters, which for 5.1 multichannel information is only abouthalf the available bit rate of 44.1 kbps. The entire space in thesubchannels would be required for 10.1 multichannel information.

In a preferred embodiment of the present invention, an error protectioncoding is therefore used to subject the additional data, which is notnormally not error-protection coded, to an error-protection codingbefore it is written into the subchannels, the error-protection codingbeing undone during playback, and serving, in particular, to correctread-out errors.

FIG. 2 shows an inventive reproduction device initially including, likea normal CD player, a means 20 for reading out the stereo channels.However, in addition to a normal CD player, a means 22 for reading outthe multichannel parameter information is provided which, however, isonly a supplementary means, if the CD player is not yet configured toread out the subchannels, or if the parameter information is stored atother locations of the CD, i.e. is not stored at the subchannels but atone or several separate sessions at the end of the CD or in a datadomain of a hybrid CD and/or hybrid partition, etc.

Connected downstream from means 22 is a means 24 for reconstructing amultichannel output which is provided at a multichannel output 26. Inaddition, a CD recognition means or an external control 28 which ismanual or taken over by another device is provided for actuating achangeover switch 30. If it is recognized that the CD includes stereoinformation only, the output of means 20 for reading out the stereochannels will be directly switched through to a stereo output 32 byswitch 30. If the CD recognition means 28 recognizes, however, that whatis dealt with is an audio CD with multichannel data, e.g. in thesubchannels, the output of means 20 for reading out the stereo channelswill be switched over by switch 30 and fed to means 24 forreconstructing, such that a multichannel output is generated, and suchthat no or only one additional stereo output is provided at output 32.

It shall be noted that switch 30 in FIG. 2 may also be replaced by abranching, so that both the normal stereo signal (e.g. via an analogoutput of the player or via a first digital output of the player) andthe stereo signal including the multichannel information may be outputin parallel via a digital output which is normally present with CDplayers and is provided for this purpose. The inventive expansion box ismounted at this digital output, the expansion box then outputting, onthe output side, the reconstructed multichannel sound with more than twochannels.

Such a playback device is thus capable of a stereophonic reproductionor, when decoding the parametric multichannel data, of reproducing asound with more than two channels, i.e., for example, a 5.1 surroundsound.

Depending on the circumstances, the inventive method for writing onto acompact disk or for playing back a compact disk may be implemented inhardware or in software. Implementation may occur on a digital storagemedium, in particular a disk or CD with electronically readable controlsignals which can interact with a programmable computer system such thatthe method is performed. Generally, the invention thus also consists ina computer program product with a program code, stored on amachine-readable carrier, for performing an inventive method, when thecomputer program product runs on a computer. In other words, theinvention may thus be realized as a computer program having a programcode for performing the method, when the computer program runs on acomputer.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents whichfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing the methods andcompositions of the present invention. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

1. An apparatus for writing audio information, from which a multichannelaudio representation may be reconstructed, onto a compact disc, theapparatus comprising: a writer for writing parametric multichannelinformation onto one or several locations of the CD which are not usedfor two base channels including a two-channel representation of theaudio information, the parametric multichannel information beingconfigured such that, together with the two base channels, it enables amultichannel audio representation with more than two audio channels. 2.The apparatus as claimed in claim 1, wherein the CD already has the basechannels before the parametric multichannel information is written bythe writer.
 3. The apparatus as claimed in claim 1, wherein the writeris further configured to write, starting from a CD without audioinformation, both the two base channels and the parametric multichannelinformation.
 4. The apparatus as claimed in claim 1, wherein the basechannels are stereo channels and are written, in accordance with the CDstandard, on the CD so that a reproduction of the two base channels instereo is possible using a CD reproduction device configured inaccordance with the CD standard.
 5. The apparatus as claimed in claim 1,wherein the writer includes a coder for error-protection coding theparametric multichannel information, so that the writer is configured towrite error-protection coded parametric multichannel information ontothe compact disc.
 6. The apparatus as claimed in claim 1, wherein thewriter is configured to write the parametric multichannel informationinto an R, S, T, U, V or W subchannel in accordance with the CDstandard.
 7. The apparatus as claimed in claim 1, wherein the writer isconfigured to write the parametric multichannel information onto a freearea following an end or prior to a beginning of a data recording takenup by the two base channels.
 8. The apparatus as claimed in claim 1,wherein the CD is a hybrid CD with a data domain, and wherein the writeris configured to write the parametric multichannel information into thedata domain of the CD, whereas the base channels are written in an audioCD area.
 9. A compact disc comprising audio information, the audioinformation including two base channels and parametric multichannelinformation, wherein the multichannel information is written ontolocations on the compact disc which are not taken up by the two basechannels, the parametric multichannel information being configured suchthat, together with the two base channels, it enables a multichannelaudio representation with more than two audio channels.
 10. An apparatusfor playing back a compact disc with audio information, the audioinformation including two base channels and parametric multichannelinformation, wherein the multichannel information is written ontolocations on the compact disc which are not taken up by the two basechannels, the parametric multichannel information being configured suchthat, together with the two base channels, it enables a multichannelaudio representation with more than two audio channels, the apparatuscomprising: a reader for reading out the two base channels and forreading out the parametric multichannel information; and a reconstructorfor reconstructing a multichannel representation on the basis of the twobase channels and the parametric multichannel information.
 11. A methodfor writing audio information, from which a multichannel audiorepresentation may be reconstructed, onto a compact disc, the methodcomprising: writing parametric multichannel information to one orseveral locations of the CD which are not provided for two base channelswhich include a two-channel representation of the audio information, theparametric multichannel information being configured such that, togetherwith the two base channels, it enables a multichannel audiorepresentation with more than two audio channels.
 12. A method forplaying back a compact disc with audio information, the audioinformation including two base channels and parametric multichannelinformation, wherein the multichannel information is written ontolocations on the compact disc which are not taken up by the two basechannels, the parametric multichannel information being configured suchthat, together with the two base channels, it enables a multichannelaudio representation with more than two audio channels, the methodcomprising: reading out the two base channels and reading out theparametric multichannel information; and reconstructing a multichannelrepresentation on the basis of the two base channels and the parametricmultichannel information.
 13. A computer program having a program codefor performing the method for writing audio information, from which amultichannel audio representation may be reconstructed, onto a compactdisc, the method comprising: writing parametric multichannel informationto one or several locations of the CD which are not provided for twobase channels which include a two-channel representation of the audioinformation, the parametric multichannel information being configuredsuch that, together with the two base channels, it enables amultichannel audio representation with more than two audio channels,when the program runs on a computer.
 14. A computer program having aprogram code for performing the method for playing back a compact discwith audio information, the audio information including two basechannels and parametric multichannel information, wherein themultichannel information is written onto locations on the compact discwhich are not taken up by the two base channels, the parametricmultichannel information being configured such that, together with thetwo base channels, it enables a multichannel audio representation withmore than two audio channels, the method comprising: reading out the twobase channels and reading out the parametric multichannel information;and reconstructing a multichannel representation on the basis of the twobase channels and the parametric multichannel information, when theprogram runs on a computer.